I'm not sure whether Bourbon Lore is the right place for this, but ultimately it's a question of bourbon history, so.

I purchased the ebook edition of "But Always Fine Bourbon". In it, Sally VanWinkle Campbell quotes an article from Life Magazine of May 24, 1937 that documents the VanWinkle family's Derby Day celebration, and makes a great point of mentioning that the VanWinkle mint julep calls for 17 year old stock, either Old Fitzgerald or Old Mammoth Cave.

Hang on a second.

Seventeen year old stock in 1937 would have to have been distilled in 1920, which couldn't have legally happened because the Volstead Act was in effect and the US government would not permit "distilling holidays" for several years thereafter. 1937 would have marked the first bottling (in bond) of any Old Fitzgerald made for Pappy at A. Ph. Stitzel after Repeal, and after he'd bought the brand from S. C. Herbst. (Stitzel-Weller itself wasn't built until 1935, so none of its distillate would have even come of age by 1937.)

The only thing I can think of is that this 17 year old stock was pre-Prohibition whiskey that Stitzel had made, or Stitzel or Weller had acquired during Prohibition and eventually bottled for private stock after 17 years in the wood. But that seems an oddity, since obviously such whiskey would be rare as hen's teeth by 1937, and it doesn't seem to me that such would be available to the public in 1937, four years after Repeal.

Prof Veach and other historian folk, have you any clue as to what this entailed?

The answer is quite simple: There was plenty of the bourbon bottled at 17 years of age from prohibition on the market. Most people considered it to woody and over aged and prefered lighter whiskey from Canada or Scotland than this "Medicinal" whiskey. Just think of how much of this 17 year old whiskey is still found and it will give you an idea of how much was available in 1937.